Jetstar is a profit centre of Qantas trying to wring as much profit out of an LCC operation as possible.
QFF is a separate profit centre and one of Qantas' largest profit contributors, which no doubt charges a hefty price for QFF points to Jetstar which eats into Jetstar's divisional profits. I'm sure that 'incentivises' Jetstar to avoid crediting your points as much as they can get away with.